Generally, a fuel cell generates electricity through an electro-chemical reaction between hydrogen supplied to a fuel electrode and air supplied to an air electrode. The electrochemical reaction between the hydrogen and the air is derived by an electrolyte membrane that is disposed between the air electrode and the fuel electrode. A fuel cell that has a solid type electrolyte membrane is generally called a polymer electrolyte fuel cell (PEFC), or a solid polymer electrolyte fuel cell.
The electrolyte membrane of a PEFC is generally made of a poly(tetrafluoroethylene) based ionomer, such as Nafion (registered trademark) of DuPont Co.
The normal operating condition of the electrolyte membrane is preferably between normal ambient temperature and 80° C., more preferably, between 55 and 65° C., and temperatures of the fuel and the oxidizing gas are preferably similar to body temperature, more preferably within a temperature difference of 10° C. In addition, an amount of supplied hydrogen (fuel gas) is preferably 1.7 to 2.0 times of a theoretical amount thereof, and an amount of supplied air (oxidizing gas) is preferably 1.2 to 1.5 times of a theoretical amount thereof. Meanwhile, the PEFC is an energy generating device having a low-voltage and high-current characteristic, and a theoretical maximum output voltage of a unit cell is 1.23V in an open-circuit state. However, a plurality of unit cells must be used for a power source of a vehicle, and it is preferable that power in a voltage range of 0.4˜0.9V is used for the unit cell to provide reasonable energy conversion efficiency of the fuel cell.
However, in a normal operating range of a PEFC, the fuel cell output can be mainly determined by movements of electrons and ions generated during the electrochemical reaction of the fuel cell. In particular, such electron and ion flow relates to a passage or movement of protons.
Therefore, initial activation of a fuel cell, i.e., to make sufficient passage of protons before a normal operation phase of the fuel cell, just after manufacturing the fuel cell, is needed, in order to achieve an efficiency of the fuel cell in a short time even if the fuel cell does not operate for a long time.
In a conventional method for initial activation, load that is continuously changed according to a load changing curve, and load cycles according to a forward load changing curve and a reverse load changing curve are alternately applied several times.
However, in such a conventional method for fuel cell initial activation of the fuel cell, the operation must be continuously performed for more than a day, and the extent of passages produced for protons also can be limited.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.